Voice-operated relay system



J. D. HILL in 2,980,827

April 18, 1961 VOICE-OPERATED RELAY SYSTEM Filed May 21, 1959 VOICE 3 l3 EMA/5.010771%; 2 f4 C/ECUIIS 40210 Fezaunvcr l?cr/ /e1e flMPL/F/EE 17 IN V EN T 0R.

VOICE-OPERATED RELAY .SYSTEM John D. Hill III, Richardson, Tex., assignor to Collins Radio Company, Cedar Rapids, Iowa, a corporation of Iowa Filed May 21, 1959, Ser. No. 814,754

2 Claims. (Cl. '317-"148.S)

This invention pertains to voice-operated relay circuits and particularly to circuits that utilize the .Miller voltage integrating ,principle as applied to electronic discharge devices in order .to .provide fast-operate .and slow-release operation of relays.

The relay circuits described herein are applicable to voice-operated circuits in radio communication circuits but may be used in any circuits wherever the application of electrical signal is to cause current flow to be started instantaneously but to be sustained for .an'interval after the signal is removed. The switching from receiving operation to transmitting operation in communication circuits is accomplished most conveniently by a voice-operated relay.

In order to receive amessage'in full and continuously, the voice-operated relay must operate instantly in response to the first syllable ofthe voice that is to be transmitted. Operation of the relay enables transmitting circuits and disables receiving circuits. The relay must 'be slow to release so as to prevent interruption of the message and relay chatter which might result if the relay were allowed to release between syllables.

In a prior circuit in which a magnetic relay is controlled by an electronic tube, an input control circuit is connected to the grid of the tube and a relay is connected to the anode of the tube. When the'relay operates in response to a signal being applied to the grid, the relay not only prepares transmitting circuits but also connects a capacitor in parallel with an input grid circuit. The connecting of the capacitor increases the time constant of the input circuit of the tube to prevent immediate releasing of the relay. The improved circuit described herein is simple, positive in operation and has the compactness that is desirable in presently designed communication equipment.

' An object of the present invention is to provide a compact relay circuit with fast-operate time and slowrelease time.

A feature of this invention is the effective application of the Miller voltage integrator principle through a feedback circuit that includes a capacitor and a diode con nected in series between the output and the input of a transistor relay control circuit.

The following description and the appended claims may be more readily understood with reference to the single accompanying drawing which shows a schematic diagram of the relay control circuit. Magnetic relay 1 operates inresponse to a message being spoken into microphone 2. Microphone 2 is connected to the input of audio-frequency amplifier 3 which may comprise a plurality of cascaded stages of audio-frequency amplification. In order that relay 1 will operate only in response to the desired message, it is desirable that ampli-- tier 3 contain a signal-operated electronic gate. The gate will then conduct only signals above a predetermined level so that unwanted background noise that is below this level will be inelfective in developing voltage in the output circuit of amplifier 3.

nited States Patent The output of amplifier 3 is connected to rectifier 4.

In :response to the input signal being above the predetercircuit :of a type NPN transistor 7. The input circuit of transistor 7 includes theemitter 8 which is connected through the resistor 9 to ground. The collector v10 in the output circuit. of the transistor is connected through winding 11 of relay 1 to a source of positive voltage.

A negative feedback circuit includes diode 12 and ca- ;pacitor 13 that are connected in series between collector 10 and base 6. The anode of diode 12 is connected to ;the collector and the cathode of the diode is connected to the junction of resistors 14 and 15 :for providing a bias to-cause diode 12 to be nonconductive when no signal'is being .appliedfrom the output of audio-frequency amplifier 3. Resistors-Hand 15 are connected in series between the source of positive voltage and ground.

Operation of relay 1 closes contacts 16 for enabling voice transmitting circuits. In order to protect a .tran .sistor 7 from voltage surges, breakdown junction diode .17 and capacitor :18 .are connected in parallel between the .collector 10 of transistor 7 and ground.

Transistor 7 is normally biased so that it is nonconductive when no signal is being applied from audio-frequency amplifier 3. Diode 12 is also biased so that it is nonconductive. In one particular circuit the voltage of the positive voltage source is 26 volts. Resistors 14 and 15 which supply the bias for diode 12 are selected so that while the voltage applied to the anode is 26 volts, the voltage that is applied to the cathode is approximately 19 volts. When the signal that is applied to the input of the audio-frequency amplifier 3 has an amplitude above a predetermined level, a gate within the amplifier operates to apply an alternating-current signal voltage to rectifier 4. This signal is rectified for applying a positive voltage to the base 6 of transistor 7. Increasing current flow in the emitter and collector circuits operates relay 1. The circuit for operating the relay includes the positive voltage source, winding 11 of relay 1, emitter 10, collector 8, and resistor 9 to ground. Operation of relay 1 closes contacts 16 for enabling transmitting circuits.

Because of the voltage drop across Winding 11, the voltage on the anode of the junction diode 12 decreases. When the relay operates, the voltage on the anode of diode 12 is lower than the voltage on the cathode. The diode 1|2, therefore, becomes conductive and completes a circuit for decreasing the charge on capacitor 13 which had been charged from the source of voltage through resistor 15 and the input circuit of transistor 7. The discharge current from capacitor 13 flows through the parallel connected resistor 5 and the base-emitter circuit of transistor 7 to operate in opposition to the voltage applied from rectifier 4. However, transistor 7 remains conductive until the signal level that is applied to the input of audio-frequency amplifier 3 falls below the predetermined threshold level.

When there is a pause in a message that is being applied to the input of audio-frequency amplifier 3, the rectifier 4 ceases to develop positive voltage for application to base 6 of transistor 7. However, the charging current for capacitor 13 through resistor 5 and the base circuit of transistor 7 maintains the transistor conductive. The continued collector current fiow caused by the charging current for an interval after the removal of signal to the input of audio amplifier 3 maintains relay 1 operation. If the interruption is only momentary as between syllables, the current flow from capacitor 13 will maintain transistor 7 conductiveuntil positive voltage is again applied from the output of rectifier 4.

If the relay circuit is to operate over a wide temperature range, it is recommended that resistor 9 that is connected between emitter 8 and ground he removed and a silicone type diode be substituted therefor. A diode having a forward voltage drop of 0.6 volt operates satisfactorily in a system to which positive 26 volts is applied through winding 11 to collector 10.

After the signal has ceased and capacitor 13 reaches nearly full charge, diode 12 again becomes nonconductive and the current flow through transistor 7 ceases abruptly as the base voltage drops below cutofi. The self-induction of winding 11 of relay 1 at the instant of cutoff develops a transient voltage which is absorbed by capacitor 18 and when the voltage across capacitor 18 rises above the breakdown voltage of breakdown junction diode 17, current is discharged through the diode to ground. Diode 17 is connected for conducting current in a reverse direction and in the particular application that has the positive source of 26 volts the junction diode may be of the type that breaks down at 34 volts.

The interval that relay 1 will be maintained closed after the input to the signal has been removed, may be determined by the capacitance of the capacitor that-is placed in the circuit for capacitor 13.

Although this invention has been described with respect to a particular embodiment thereof, it is not to be so limited, as changes and modifications may be made therein which are within the spirit and the scope of the invention as defined by the appended claims.

What is claimed is:

1. A voice-operated relay comprising, a transistor having a base, an emitter and a collector, a source of potential having two terminals, a magnetic relay having a winding connecting said collector to one terminal of said source, a feedback circuit comprising a diode and 2. capacitor connected in series between said collector and said base, said diode being connected to said collector,

a voltage divider connecting said source to the junction of said diode and said capacitor for biasing said diode nonconductive, means responsive to the application of audio-frequency signal above a predetermined level for applying rectified audio-frequency signal to said base, means for normally biasing said base beyond cutofi relative to said emitter to prevent substantial current flow through said transistor, said transistor becoming conductive in response to the application of rectified audio signal to said base for operating said relay, said diode becoming conductive and the voltage applied across said capacitor decreasing in response to the voltage drop across the winding of said magnetic relay caused by the current flow through said transistor, and said capacitor recharging in response to an interruption in said rectified audio-frequency signal to maintain said transistor conductive and thereby to maintain said relay operated for an interval during which insuflicient rectified audio-frequency signal is applied to said base for maintaining said relay operated.

2. A voice-operated relay as claimed in claim I having a voltage breakdown diode connected between said collector and the other terminal of said source of supply to prevent destructive surges of current caused by selfinduction of said relay winding from damaging said transistor.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Anderson: Radio & Television News, pages 57 and 98, May 1951. 

